From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from localhost (localhost [127.0.0.1]) by turing.freelists.org (Avenir Technologies Mail Multiplex) with ESMTP id 48959276E6 for ; Mon, 16 Jul 2018 09:15:43 -0400 (EDT) Received: from turing.freelists.org ([127.0.0.1]) by localhost (turing.freelists.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id jHfEryZNE6po for ; Mon, 16 Jul 2018 09:15:43 -0400 (EDT) Received: from smtp40.i.mail.ru (smtp40.i.mail.ru [94.100.177.100]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by turing.freelists.org (Avenir Technologies Mail Multiplex) with ESMTPS id F25DA26F76 for ; Mon, 16 Jul 2018 09:15:42 -0400 (EDT) Subject: [tarantool-patches] Re: [PATCH v1 1/1] lua: fix strange behaviour of tonumber64 References: <6b638fd3-58bc-2ed7-c32c-3f0a440d1f2b@tarantool.org> <20180716124949.3uhj5zrkivphdnaw@tkn_work_nb> From: Vladislav Shpilevoy Message-ID: Date: Mon, 16 Jul 2018 16:15:39 +0300 MIME-Version: 1.0 In-Reply-To: <20180716124949.3uhj5zrkivphdnaw@tkn_work_nb> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: tarantool-patches-bounce@freelists.org Errors-to: tarantool-patches-bounce@freelists.org Reply-To: tarantool-patches@freelists.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: tarantool-patches List-subscribe: List-owner: List-post: List-archive: To: Alexander Turenko Cc: Kirill Shcherbatov , tarantool-patches@freelists.org On 16/07/2018 15:49, Alexander Turenko wrote: > Hi, Vlad! > > That is interesting discussion. Hope you don't mind my participation. Hi! Your participation is appreciated! > > WBR, Alexander Turenko. > > On Mon, Jul 16, 2018 at 01:23:36PM +0300, Vladislav Shpilevoy wrote: >> Thanks for the patch! See 4 comments below. >> >> On 13/07/2018 14:21, Kirill Shcherbatov wrote: >>> Function tonumber64 has worked incorrectly with values less >>> than LLONG_MIN. >>> Now it works in the interval [LLONG_MIN, ULLONG_MAX] returning >>> nil otherwise. >>> >>> Closes #3466. >>> --- >>> Branch: https://github.com/tarantool/tarantool/compare/kshch/gh-3466-tonumber64-strange-behaviour >>> Issue: https://github.com/tarantool/tarantool/issues/3466 >>> >>> src/lua/init.c | 6 +++++- >>> test/box/misc.result | 19 +++++++++++++++++++ >>> test/box/misc.test.lua | 8 ++++++++ >>> 3 files changed, 32 insertions(+), 1 deletion(-) >>> >>> diff --git a/src/lua/init.c b/src/lua/init.c >>> index 9a96030..4b5285d 100644 >>> --- a/src/lua/init.c >>> +++ b/src/lua/init.c >>> @@ -222,7 +222,11 @@ lbox_tonumber64(struct lua_State *L) >>> if (argl == 0) { >>> lua_pushnil(L); >>> } else if (negative) { >>> - luaL_pushint64(L, -1 * (long long )result); >>> + if (result > -((unsigned long long )LLONG_MIN)) { >> >> 1. Please, do not enclose one-line bodies into {}. >> >> 2. How can you cast LLONG_MIN (that is negative) to the unsigned type? >> > > Cast does not change bits. It is legal. Yes, technically it is legal, but casting negative value to an unsigned type looks weird. > >> 3. Why not 'result > LLONG_MAX'? As I understand, abs(LLONG_MAX) == abs(LLONG_MIN), >> it is not? (http://www.cplusplus.com/reference/climits/) >> > > No, LLONG_MAX is 2^63-1, but LLONG_MIN is -2^63. We want to compare > result with 2^63. We are trying to do so in platform-independent way > (hovewer unsiged unary nimus equivalence with signed one is likely > two-complement number representation property and can be violated on > other platforms). > > Are you think we should introduce our own constant > 9223372036854775808ULL (2^63) and avoid that complex assumptions set? It Ultimately no. We should not invent the constants. > would be explicitly number-representation-dependent, so maybe it is > better. Ok. Logically we want an error on -result < INT64_MIN, right? It is the same as result > -INT64_MIN. But we can not say -INT64_MIN because abs(INT64_MIN) > INT64_MAX, yes? Then lets rephrase the comparison: result > -INT64_MIN | v result + 1 >= -INT64_MIN | v result >= -INT64_MIN - 1 | v result >= -(INT64_MIN + 1) <- that is the solution. As I understand, -(INT64_MIN + 1) is exactly 2^63 - 1 and fits in int64, right?